I have a misfiring 96 Chevy Blazer, 4WD, 4.3 liter. Its recurred

Customer Question

I have a misfiring 96 Chevy Blazer, 4WD, 4.3 liter. It's recurred 2 or 3 times in the last 6 months now. I replaced plugs, wires, replaced intake manifold gasket, new distributor and a new cylinder 3. I've had it read as multiple misfire and later as cylinder 3 misfire. Something is wrong and I want to get to the bottom of it without replacing everything.

Have the injectors been replaced or at least cleaned to see if the misfire changed? These engines are known for the spider assembly or fuel injection unit under the upper intake manifold to become restricted that can cause misfires at random times or all the time on certain cylinders.

First time it misfired I brought it to a guy... he replaced the distributor...The time I brought in my car due to multiple misfiring, the mechanic recommended, new sparkplugs and wires, intake manifold gasket was leaking, and that I should clean the injectors. So I had him clean the injectors and replace the manifold gasket and my brother and I did those plugs and wires. About a month later it starts doing it again and I brought it in and he did work on the misfiring 3rd cylinder that time which cost a couple hundred

Well it starting re-doing it a few days ago and I haven't stopped anywhere to have to code tested yet, but I had that done in beginning/middle of June and it ran fine until this past week. When I start my car sometimes it'll be shakey and the check engine light will flash, but then when I drive most the time it stops and runs fine while the light will stay solid.. Other times I'll be driving and it'll flash, then stop for a few seconds then flash again and keep going flashing my whole ride (15 mins or so). Then yesterday it ran fine with the light on for a half hour then started to misfire again at about half hour/35 mins when I was near my destination, then ran fine all the way back home from there

Customer:replied 5 years ago.

A couple of days ago I smelled a (strong enough to make me stop the car and look under the hood) sulfuric smell when I gave it some good throttle to get going.

Ok, it may or may not be the same cylinder misfiring. You need to have the engine scanned to see what trouble codes are setting. It may be weak fuel pressure, other cylinders misfiring because of restrictions in the poppets to those cylinders or it may be the catalytic converter restricted as these vehicles are known for that also.

The entire spider updated design is $400-500 plus gaskets. That smell could be from a rich or lean condition from the engine running. If the poppets are sticking open that would definitely cause a rich condition that allows raw fuel thru the engine and into the converter (hence the egg/sulphur smell).

If there's still misfires on all cylinders suspect the injection unit. Also, the cat converter could cause cylinder misfires but fail because of the injectors. I would replace the injector unit and then perform an exhaust back pressure test to see if there's any restrictions in the cat converter (anything over 1 psi at 1000 RPM is too much and indicates a restricted cat converter).

If it were my vehicle and the cause was the spider assembly I would replace the entire unit to the updated unit. Once they are upgraded I have never seen a repeat failure. This eliminates the potential for having to keep replacing each poppet one at a time.

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